1. Field of the Invention
The present invention relates to a motor-driven hammer having an impact mechanism that is driven by the motor via a crank drive. The hammer has a protective cover that is provided with handgrips and is cushioned relative to the housing of the hammer. When viewed in the upright position of operation of the hammer, the cover covers, and is spaced from, the top, both sides, and the front of the motor and the crank drive, at least relative to an operator. With hammers of this general type, the task of the cover is to protect the operator from heat radiating from the hot motor parts, and from direct contact with these parts. The cover is also intended for muffling radiation of noise from the motor into the environment, and especially to the operator. In addition, the cover protects the operator from current pulses, which with apparatus of this type can be caused, for example, by striking an underground cable with the bit during breaking-up operations, or, with electric hammers, by carelessly damaging the actual electrical lead on the motor, thus conveying dangerous voltage to the motor parts of the hammer. Furthermore, by disposing the handgrips for guiding the hammer on the protective cover, the latter fulfills the additional task of cushioning the grip, and hence of avoiding damaging the health of the operator and of increasing the operating comfort for the latter.
2. Description of the Prior Art
With the heretofore known hammers of the aforementioned general type (German Offenlegungsschrift No. 30 35 351), the protective cover is supported at a number of locations on the hammer housing via simple springs. As a result, under certain operating conditions, the cover can twist or tilt relative to the housing. The cover is then in direct contact with the housing, and to a large extent loses its ability to fulfill the aforementioned tasks. With the heretofore known hammers, the ability of the protective cover to function is also extensively impaired as the operating pressure exerted upon the handgrips by the operator increases. The same is true for pulling upon the handgrips, which is done by the operator when he tries, with the hammer, to again pull out a bit that has become jammed, for example in working in concrete. In these cases, the cause for the reduction of the ability of the cover to function is the spring force of the simple springs between the cover and the housing which spring force increases very sharply and linearly already with comparatively small relative movements between the cover and the housing. These simple springs must be very strong so that contact between the motor housing and the protective cover cannot already occur under normal operating conditions. If the springs are too weak, or even if extreme pressure or pulling is exerted upon the cover via the handgrips, the known dangerous jarring blows can occur even without direct contact between the cover and the housing. These jarring blows are transmitted from the hammer, via the completely compressed springs, to the protective cover as spring block shocks.
An object of the present invention therefore is to provide a hammer of the aforementioned general type that is designed in such a way that the protective cover has no possibility of coming into contact with the hammer housing, that both the left and the right handgrip are always uniformly cushioned independent of the size of the operator, that jarring blows of the cushioned cover with the housing are precluded even under high pressures and pulling forces exerted by the operator upon the handgrips, and that nevertheless the cushioning of the handgrips is very soft in the normal operating range during customary applications, so that the operator can hardly feel any vibration.